1. Field of the Invention
This invention relates generally to an apparatus and a method for measuring crimp characteristics of fibers; more specifically, an apparatus and method for characterizing fibers in a moving crimped tow.
2. Description of the Prior Art
Manufactured or synthetic fiber filaments are usually crimped into a tow before being cut into staple for further processing for various uses such as tops, slivers or yarns. The fibers are usually crimped by passing the fibers through a crimping apparatus to produce waves or crimps The quality of manufactured fibers is often measured by crimp characteristics such as crimp uniformity, number of crimps per inch, crimp frequency, etc. Until recently, the crimp properties have been measured by manual examination of a cut portion of fiber, for example, by counting the number of crimps per unit length.
It follows that automated systems for measuring crimp characteristics would greatly improve the speed and accuracy in characterizing the fibers, enabling on line adjustments in the production process, and the production of fiber staple according to specifications.
Various types of automated systems for measuring crimp characteristics have previously been proposed. Generally, the systems include a light source for illuminating the crimped tow; a photographic element for acquiring an image of a portion of the crimped tow; circuitry for processing the acquired image; and a display for displaying the measured crimp characteristics.
One type of system employs a conventional TV camera to acquire the image of the moving crimped tow. As is apparent to one skilled in the art, a TV camera captures an image pattern and converts the image as electrical charges corresponding to the brightness levels of the moving crimped tow. The charges are converted to a video signal in a sequential order of picture elements. The picture elements are displayed on a monitor as an interlaced raster scan, e.g., the picture elements are swept horizontally from top to bottom. In interlaced scanning, two fields are used.
After completion of the first field scan from top to bottom, the beam is blanked as it returns to the top where the process is repeated to provide a second field scan. Due to the half-line offset for the start of the beam return to the top of the raster and for the start of the second field, the lines of the second field line lie in between the lines of the first field. Thus, the lines of the two are interlaced. The two interlaced fields constitute a single video frame.
A problem exists with using a conventional TV camera to acquire images of a moving crimped tow. The acquired image is not a true representation of the actual image, because the tow is moving. The two fields which are interlaced are obtained from two different areas of the tow. By the time the beam returns to the top of the raster to start scanning the second field, the tow has moved and a different portion of the tow is scanned. Therefore, measured results derived from the interlaced images depart from the true images.
A common approach used to counteract the above problem associated with the use of a conventional TV camera is by use of a synchronized strobing system. A stroboscopic light source emits a light pulse which creates an apparent stopped motion view of the moving crimped tow. The camera is synchronized to take a snap shot of the moving crimped tow when the light pulse is emitted. A synchronized strobing system effectively freezes the moving crimped tow and the two interlaced fields do not produce an erroneous image as in using a non-strobed system. However, advanced electronics are required for the synchronization controls. Further, in order to cover an entire width of the moving tow when using a synchronized strobing system, movement of the focused strobe light source and/or the camera may be necessary, and positioning mechanisms such as stepping motors and controls are involved. If light or camera movement is required, extra time is needed to position the devices, making on-line or real-time measurements and/or device adjustments difficult if not impossible. Examples of strobed-based apparatus for measuring crimp characteristics of fibers in a moving crimped tow are disclosed in U.S. Pat. Nos. 4,737,846; 4,415,926; 4,232,336; and 4,240,110
A need therefore exists for an apparatus which uses a continuous or non-strobed system for acquiring images of a moving crimped tow which is devoid of the above problems and is also capable of on-line or real-time measurements and/or system adjustments.